Varifocal objectives as used in photographic or cinematographic zoom cameras, e.g. those designed for motion-picture film of the Super-8 type, conventionally consist of a four-component front group of adjustable magnification ratio juxtaposed with a rear group composed of several air-spaced lenses, the rear group constituting a fixed-focus basic objective to which the front group is permanently or removably attached. The two groups are generally separated by a diaphragm space which may also contain a reflex prism.
The varifocal front group usually consists of a stationary positive first component (which may be axially adjustable for focusing purposes), an axially shiftable negative second component which may be referred to as a variator, an axially shiftable negative third component which may be termed a compensator, and a stationary positive fourth component next to the diaphragm space.
By a suitably correlated axial displacement of the two negative components, the overall focal length of the system can be changed between a maximum value f.sub.max and a minimum value f.sub.min without any dislocation of the image plane of the objective.
Different varifocal ratios f.sub.max : f.sub.min can be obtained with the same basic objective and the same image-side half of the adjustable front group, i.e. the third and fourth components of that group, by substituting different lenses or lens combinations for the first two components of that group. Thus, only the object-side half of the front group of such an optical system needs to be interchangeable in order to provide a set of varifocal objectives of different zoom ranges.